On 1/28/21 3:58 AM, Jakub Jelinek wrote:
Hi!
We emit a bogus warning on the following testcase, suggesting that the
operator should return *this even when it does that already.
The problem is that normally cp_build_indirect_ref_1 ensures that *this
is folded as current_class_ref, but in templates (if return type is
non-dependent, otherwise check_return_expr doesn't check it) it didn't
go through cp_build_indirect_ref_1, but just built another INDIRECT_REF.
That seems like a bug in build_x_indirect_ref.
Which means it then doesn't compare pointer-equal to current_class_ref.
The following patch just checks if it is the same thing like
cp_build_indirect_ref_1 would check if it would be called.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2021-01-27 Jakub Jelinek <ja...@redhat.com>
PR c++/98841
* typeck.c (check_return_expr): If processing_template_decl, don't
rely on *this expression being always pointer-equal to
current_class_ref.
* g++.dg/warn/effc5.C: New test.
--- gcc/cp/typeck.c.jj 2021-01-25 10:02:28.380126847 +0100
+++ gcc/cp/typeck.c 2021-01-27 11:21:13.117875551 +0100
@@ -10188,6 +10188,19 @@ check_return_expr (tree retval, bool *no
/* Returning '*this' is obviously OK. */
if (retval == current_class_ref)
warn = false;
+ /* In templates, '*this' might not compare pointer equal to
+ current_class_ref. */
+ else if (processing_template_decl
+ && retval
+ && TREE_CODE (retval) == INDIRECT_REF
+ && (TREE_OPERAND (retval, 0) == current_class_ptr
+ || (TREE_CODE (TREE_OPERAND (retval, 0)) == NOP_EXPR
+ && (TREE_OPERAND (TREE_OPERAND (retval, 0), 0)
+ == current_class_ptr)
+ && (same_type_ignoring_top_level_qualifiers_p
+ (TREE_TYPE (TREE_OPERAND (retval, 0)),
+ TREE_TYPE (current_class_ptr))))))
+ warn = false;
/* If we are calling a function whose return type is the same of
the current class reference, it is ok. */
else if (INDIRECT_REF_P (retval)
--- gcc/testsuite/g++.dg/warn/effc5.C.jj 2021-01-27 11:24:34.451565246
+0100
+++ gcc/testsuite/g++.dg/warn/effc5.C 2021-01-27 11:23:23.836375556 +0100
@@ -0,0 +1,17 @@
+// PR c++/98841
+// { dg-do compile }
+// { dg-options "-Weffc++" }
+
+struct S {
+ template <typename T>
+ S& operator=(const T&) { return *this; } // { dg-bogus "should return a
reference to" }
+ S& operator=(const S&) { return *this; }
+};
+
+void
+foo ()
+{
+ S s, t;
+ s = 1;
+ s = t;
+}
Jakub
